[Kirby64]

I'm going to disagree with you. CI/CO is absolute. The issues people get stuck on is twofold:

Calories in is largely correct, however it comes with a few small cavaets. If you eat an excess amount of food (and I mean a LOT, 6000cal+), you probably cannot disgest all of it. For normal sane amounts of calories you're going to digest the vast majority of them. For certain folks, they may have trouble digesting certain types of food. This is going to impact far fewer people than most think, I believe.

The much bigger one is calories out. What you burn can change a lot. Certain bodies adapt their calorie burn quite quickly to calorie reduction. Unconscious effort changes can heavily increase or reduce calorie usage.

There's very little about sugar that inherently makes it "constantly store energy" for certain people. Its calories like anything else, and if you eat tons of it, it's just tons of calories.

The final note is that certain people can have huge swings in water retention depending on food eaten. Salty foods do this for most people. But that isn't true weight gain, and should be largely ignored.